A large number of derivatives of monofunctional methacrylic acid esters and polyfunctional methacrylic acid esters are known, and some of these esters are commercially produced and used as the starting materials for adhesives, paints, cast molding materials, and photosensitive materials, utilizing the high polymerizability thereof.
On the other hand, few derivatives of thiomethacrylic acid esters are known. For example, although phenylthiomethacrylate and 4-chlorophenylmethacrylate were synthesized by Jean Samrel et al (Journal of American Chemical Society (i. Am. Chem. Soc.), 86, 2509 (1958)], almost none of these thiomethacrylic acid esters have been utilized commercially.
In the prior art, as organic optical materials, polystyrene resins, polymethyl methacrylate resins, polycarbonate resins, and polymers of diethylene glycol and diallylcarbonate have been utilized, and since these have a desirable light weight, safety, workability, and dyeability, the demand therefore has increased.
Organic optical materials of the prior art, however, for example, polymethacrylate resins, have a high hygroscopicity as the resin characteristic, are susceptible to changes in shape or refractive index, and are unstable as optical materials. On the other hand, polystyrene resins and polycarbonate resins have drawbacks such as an optical birefringence, generation of scattered light, and loss of transparency with time. Further, the application of polymers of diethylene glycol diallylcarbonate per se as the optical material is limited due to the low refractive index (refractive index=1.499) thereof.
To eliminate these drawbacks, various resins for optical materials have been proposed, and examples of these proposals include, for example, Japanese Unexamined Patent Publications (Kokai) Nos. 57-28115, 57-28116, 59-184210, 60-7314, 60-179406, 60-217301, 60-186514, 60-166307, 60-103301, 60-124607, 62-232414, 62-235901, 62-267316, 63-15811, 63-46213, 63-72707, 63-75022, 63-113012, 63-130614, 63-130615, 63-170401, 63-170404, 63-191813, 63-248811, 63-251408t 63-268707, and 64-54021, Japanese Examined Patent Publication (Kokoku) Nos. 63-45081 and 63-45082, and Japanese Unexamined Patent Publication (Kokai) Nos. 59-164501, 60-217299, 61-16901, 62-283109, 62-287316 and 63-162702. The cured products obtained by these prior arts, however, are not satisfactory as optical materials because they are optically nonuniform, suffer from a severe weathering coloration, and lack dimensional stability.
Also, curable compositions of polyene and polythiol are disclosed in Japanese Patent Publication (Kokoku) No. 53-28959, Japanese Unexamined Patent Publications (Kokai) Nos. 53-134096, 57-125025, 57-130572, 58-80317, but in these prior arts, due to the action of the mercapto groups as the chain transfer agent, a problem arises in that the polymerization tends to proceed even under storage in a dark place. Further, when the polyene compound is a (meth)acrylic acid derivative, a mutual polymerization between polyene compounds is liable to occur, whereby the mercapto groups are left, and thus problems arise such as an insufficient curing of the polymerized cured product, a lower chemical resistance, and a non-homogeneity of the cured product.